A call forwarding service for forwarding an incoming call from a call originator terminal device to a forward destination terminal device via a forward source terminal device is well known.
According to the call forwarding service, the same user often possesses a plurality of forward source terminal devices used for relaying an incoming call.
In many cases, as explained above, the user having a plurality of forward source terminal devices makes a setting in such a way that all incoming calls to the plurality of forward source terminal devices are forwarded to the same forward destination terminal device. This allows one terminal device to collectively receive information from various forward sources.
In general, when one forward destination terminal device is attempted to collectively receive incoming calls from the plurality of forward source terminal devices, it is unclear which one of forward source terminal devices relays the incoming request from a certain call originator terminal device.
Accordingly, when the user of the forward destination terminal device views a history of received calls, and carelessly calls back (returns the call), various confusions may occur.
An example is that when the user of the forward destination terminal device makes public only a specific forward source terminal device to the outside, but desires to keep the forward destination terminal device in secret. In such a case, when a call-back is carelessly made as explained above, the presence of the forward destination terminal device is revealed to a user receiving the call-back.
On the other hand, the above-explained call-back is an incoming call from an unexpected terminal device (telephone number) for the user of the call originator terminal device. Accordingly, the user of the call originator terminal device receiving the call-back may regard that this incoming call is made from a suspicious individual, and may not answer the call.
In order to assist communication between users relating to such a call-back, there is proposed a technology which makes a setting in advance for an execution condition of requesting a call-back to display on the screen showing a history of received calls of the forward destination terminal device, when this execution condition is satisfied, a message for requesting a call-back to the call originator terminal device (see, for example, Patent Document 1).
According to the technology disclosed in Patent Document 1, however, there is no particular consideration shown to the possibility that the above-explained confusion may occur at the time of making the call-back due to that fact that it is unclear which one of the forward source terminal devices for relaying the incoming call relays an incoming request from a certain call originator